FIG. 10 is an enlarged cross-sectional view of a part of a piston pump 1 of a first prior art. The piston pump 1 includes, in a casing 2, a cylinder block which is rotatable in a rotational direction A1 around a rotational axis L1 by a rotational shaft 3. In the cylinder block, a plurality of piston chambers are formed, and cylinder ports connected to the piston chambers are formed. A piston fits in each piston chamber. Each piston is provided at a first end portion thereof with a shoe, and each shoe is pressed toward a swash plate 4 which inclines with respect to a virtual flat surface perpendicular to the rotational axis L1. In sync with the rotation of the cylinder block, each piston carries out a reciprocating displacement including an extending stroke and a retracting stroke.
The swash plate 4 is supported by a swash plate support 5 so as to be tiltable around a tilt axis L2 orthogonal to the rotational axis L1. A stroke length of each piston changes by tilting the swash plate around the tilt axis L2, and this changes the amount of hydraulic oil sucked into each piston chamber. In the casing 2, a pin 6 fits in an inner peripheral portion thereof. The pin 6 is provided such that a part thereof projects from the inner peripheral portion in a first direction along the rotational axis L1. The swash plate support 5 is attached to the casing 2 by causing the pin 6 to fit in the casing 2 in a state in which the rotational shaft 3 is inserted into the swash plate support 5. With this, the rotation of the swash plate support 5 around the rotational axis L1 is prevented. Thus, an angular displacement of the swash plate around the rotational axis L1 due to vibrations, etc. is prevented, and an unstably fixed state of the swash plate 4 is suppressed (Patent Document 1 for example).
FIG. 11 is an enlarged cross-sectional view of a part of a piston pump of a second prior art. A piston pump 10 includes a casing 11, a rotational shaft 12, a cylinder block, a plurality of pistons, a plurality of shoes, a swash plate 13 and a swash plate support 14, and is constructed in the same manner as the piston pump 1 of the first prior art. The swash plate support 14 is attached to the casing 11 in such a state that the rotational shaft 12 is inserted into the swash plate support 14. The swash plate support 14 is fastened to the casing 11 with a plurality of bolts 15 which penetrate through the casing 11 from its outer side to its inner side. With this, the rotation of the swash plate support 14 around the rotational axis L1 and the displacement of the swash plate support 14 in directions along the rotational axis L1 are prevented. Thus, the angular displacement of the swash plate around the rotational axis L1 due to vibrations, etc. and the displacement of the swash plate in the above directions caused by the displacement of the rotational shaft in the direction along the rotational axis L1 can be prevented, and the unstably fixed state of the swash plate is suppressed (See Japanese Laid-Open Patent Publication 59-90782 (page 2, FIG. 1))